On Tue 24-04-18 13:01:03, David Rientjes wrote: > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > Is there any reason why we cannot simply call __oom_reap_task_mm as we > > have it now? mmap_sem for read shouldn't fail here because this is the > > last reference of the mm and we are past the ksm and khugepaged > > synchronizations. So unless my jed laged brain fools me the patch should > > be as simple as the following (I haven't tested it at all). > > > > I wanted to remove all per task checks because they are now irrelevant: > this would be the first dependency that exit_mmap() has on any > task_struct, which isn't intuitive -- we simply want to exit the mmap. > There's no requirement that current owns the mm other than this. There is no such requirement in the __oom_reap_task_mm. The given task is used for reporting purposes. > I wanted > to avoid the implicit dependency on MMF_OOM_SKIP and make it explicit in > the exit path to be matched with the oom reaper. Well, I find it actually better that the code is not explicit about MMF_OOM_SKIP. The whole thing happens in the oom proper which should be really preferable. The whole synchronization is then completely transparent to the oom (including the oom lock etc). > I didn't want anything > additional printed to the kernel log about oom reaping unless the > oom_reaper actually needed to intervene, which is useful knowledge outside > of basic exiting. Can we shave all those parts as follow ups and make the fix as simple as possible? > My patch has passed intensive testing on both x86 and powerpc, so I'll ask > that it's pushed for 4.17-rc3. Many thanks to Tetsuo for the suggestion > on calling __oom_reap_task_mm() from exit_mmap(). Yeah, but your patch does have a problem with blockable mmu notifiers IIUC. -- Michal Hocko SUSE Labs
